Mommy, How Do We Spell "Knees"?

Lily has been interested in spelling lately. (She's so interested in spelling that she's forfeited her bath toys the last two nights and opted to play "How do you spell ....?" instead.) She's had basic phonics mastered for quite some time, and she's recently moved on to spelling. When she asks how to spell a word, I generally sound the word out for her, letter by letter, and help her out how to spell it. That strategy generally works well, but not always.... By now she understands that U is Q's best friend and that there are some words that have a silent letter, usually an E at the end. However, she managed to pick a few of the words Mommy had been dreading tonight: "eyes," "knees," and "light." While I can explain a lot of the idiosyncrasies of the English language, how does one explain the silent K or the -GHT combination to a 3-year-old?